[CS61C FA20] Lecture 12.4 - RISC-V Instruction Formats II: Summary — Transcript

Full transcript

1. 0:09And welcome back to the final episode of
2. 0:12RISC-V instruction encoding.
3. 0:15So, that was it. We have covered all six
4. 0:19types of instructions that we will
5. 0:20encounter in RV32
6. 0:24version that covers all the integer
7. 0:27operations.
8. 0:30There may be different ones
9. 0:32for different extension, but this is the
10. 0:33base that is good enough to allow us to
11. 0:37compile any C program to it.
12. 0:41That's quite amazing, isn't it?
13. 0:45The The principles that we have seen
14. 0:47here
15. 0:49are that we have sacrificed some of the
16. 0:52perhaps understandability of how
17. 0:55um the immediates are being formed
18. 1:00for ease of hardware design. So, things
19. 1:03are always placed in the same
20. 1:06same place.
21. 1:08Um registers are always in the same
22. 1:10place such that processor hardware has
23. 1:14an easier time finding them. Similarly,
24. 1:17all the immediates are placed are
25. 1:19aligned in a way that the processor will
26. 1:23generally find them in the same place.
27. 1:25And that'll make the design easier and
28. 1:28make the hardware run faster. And that's
29. 1:31worth any added complexity that we have
30. 1:34to do in remembering how these
31. 1:36instructions work.
32. 1:40There have been quite a few changes to
33. 1:42RISC-V ISA and its specification
34. 1:45from the
35. 1:47in the past 10 years since it was since
36. 1:51the project started, um we have seen
37. 1:54numerous versions. But there is
38. 1:56something that is very exciting.
39. 1:58That the
40. 2:00base and several of the
41. 2:02extensions of the RISC-V ISA have been
42. 2:05ratified. So, that means
43. 2:08that community has accepted them and
44. 2:10they've been frozen forever. They will
45. 2:12not change.
46. 2:13There is one little catch. There is a
47. 2:16lot of stuff out there that is based on
48. 2:19draft specification of RISC-V, including
49. 2:23the Patterson and Hennessy textbook. So,
50. 2:26some of the things that we will find in
51. 2:28the textbook are not exactly the same
52. 2:32how they are today. The textbook is
53. 2:34about 2 or 3 years old, and things have
54. 2:37changed since. But, they're not going to
55. 2:39be changing going forward. Um the
56. 2:42differences are really minor. Um these
57. 2:45are some of the encodings have changed,
58. 2:48and um some of the naming has changed.
59. 2:51But, in general, the principles stay the
60. 2:53same.
61. 2:54So, what we have here are all the base
62. 2:57instructions that we have in RISC-V
63. 3:00RV32I
64. 3:02ISA.
65. 3:04And that's it. We haven't covered three
66. 3:06instructions that are useful
67. 3:09for um environment calls and generally
68. 3:13operating system support and running
69. 3:16multiple threads. We don't need that. We
70. 3:18uh for now, we can run any C program
71. 3:22with the set of instructions that we
72. 3:23have for now. And that's quite exciting.
73. 3:26That will enable us
74. 3:28to run through our stack of um
75. 3:33building
76. 3:35computer uh computing systems, starting
77. 3:39from C down to assembly language,
78. 3:42machine language, and we have really now
79. 3:44understood the ISA.
80. 3:46Now,
81. 3:49after we understand how we build uh how
82. 3:51we
83. 3:52compile, compile, assemble, link, and
84. 3:54load, we're going to get into actually
85. 3:57building the hardware that can execute
86. 3:59all of this.
87. 4:00Stay tuned, and see you soon.